i tried to demo knife sharpening at a friend's place. i brought stone and strop and let him choose kitchen knives. he owned tons and chose the two worst specimen! microchipped along the entire bevel, and bent blade (righty's abuse), cheap knife, cheap metal. Even budgeteer me admitting now that it wouldn't be worth my efforts, sweat, time!
anyway, i tried to do a fast demo .. and failed. hated to give up. if you show something to others, you run out of patience too! you get nervous because everyone's patience is running out including your own.
my advice: do the demo and teaching with great quality knives only in very good condition, knives which just stopped slicing copy paper nicely. they must be free of chips and microchips. the blade stock must(!) be straight. and the blade must be stiff, non-flexible. and void of recurves. you can't teach sharpening on a 5$ WALMART knife, such a knife will ruin your lesson, impossible to get encouraging results for a beginner. cheap blade steels are soft, ductile, and too challenging to deburr cleanly by a beginner.